Nuclear reactors are becoming an increasingly necessary means of meeting the nation's energy requirements given growing concerns about traditional carbon producing methods of generating energy. A principal concern prior to the acceptance of nuclear energy is the safe management of radioactive waste during reprocessing and storage.
This concern is addressed is by utilizing nuclear reprocessing techniques, such as pyroprocessing, to extract nuclear components from the spent fuel discharged from reactors. Pyroprocessing involves dissolving spent fuel at high temperatures in a molten salt to create a molten salt electrolyte. Then the spent fuel is electrorefined in the molten salt, which essentially electroplates most or all of the actinides elements for extraction. Typically, a solid metal cathode is used to extract uranium and a liquid cadmium cathode is used to extract all actinides, including plutonium. Plutonium and uranium are focused upon because the other transuranic elements exist at much lower concentrations in the molten salt electrolyte.
In pyroprocessing, the electrorefining process must be carefully monitored to ensure that the electrochemical operation is proceeding efficiently. Specifically, monitoring the concentration ratio of Pu3+ to U3+ in the molten salt electrolyte is particularly important because electrorefining operators need to know which extraction technique is optimal. For example, the solid metal cathode is operated; uranium is extracted from the molten salt electrolyte and the Pu3+ to U3+ ratio increases. The solid metal cathode becomes increasingly inefficient as the Pu3+ to U3+ ratio increases, at which point it may become preferable to switch from operating the solid metal cathode to operating a liquid cadmium cathode. Similarly, as the liquid cadmium cathode is used, plutonium is extracted from the molten salt electrolyte. The continued use of the liquid cadmium cathode becomes increasingly inefficient as the Pu3+ to U3+ ratio decreases.
As a result, monitoring the Pu3+ and U3+ concentrations in the molten salt electrolyte is important to ensure that the refining process is efficient at collecting actinides. The current method for measuring actinides in molten salt electrolytes involves taking a sample of the highly radioactive molten salt electrolyte, transferring that radioactive sample to a laboratory, and analyzing the sample using an inductively coupled plasma mass spectrometer (ICP-MS). Sadly, the entire process generally requires a few weeks before results are obtained. Therefore, there exists a need for in-situ, real-time monitoring of actinide ion concentrations in molten salt electrolyte for pyroprocessing.